Control of air-fuel ratio

ABSTRACT

A device for controlling the air-fuel ratio in an internal combustion engine wherein the rate of fuel flow from the float chamber to the air stream in the venturi of a carburetor is modified by a pressure modifying tube joining the float chamber and the venturi, a valve in said tube being responsive to the thermal conductivity of the exhaust gases in the exhaust pipe of the engine.

United States Patent 1191 Bachle July 3, 1973 CONTROL OF AIR-FUEL RATIO 1,857,889 5/1932 Sturm 26I/D1G. 67 ,984,382 12 193 P t' 261 DIG. 67 1 inventor: Bachle, Gmsse Pomte Farms 1,993,665 3/1935 73/25 2,023,647 12/1935 Schmid 26i/DIG. 67 2,255,551 9/1941 Willenborg 73/27 R [73] 1:23 'l g Los 2,752,136 6 1956 Gardner 26i/DIG. 67 Filed: 1972 Primary ExaminerW ende11 E. Burns [2 Appl' No: 228,943 Attorney-Robert C. Hauke, Ernest 1. Gifford et a1.

[52] U.S. CL... 123/119 R; 123/119 E, 26l/DIG. 68 [57] [51] In. CL oz 7/12, z 7 A dev1ce for controlling the a1r-fue1 ratio 1n an 1nternal [58] Field of Search 123/119 R, 119 E; wmbustion engine wherein the rate of fuel flow from 73 5 261/016 67 the float chamber to the air stream in the venturi of a carburetor is modified by a pressure, modifying tube [56] References Cited joining the float chamber and the venturi, a valve in UNITED STATES PATENTS said tube being responsive to the thermal conductivity 1 702 433 2/1929 -G "ff 67 of the exhaust gases in the exhaust pipe of the engine.

r1 on 1,840,279 H1932 1 Claim, 1 Drawing Figure Sturm 261/DIG. 67

. 1- CONTROL or AIR-FUEL RATIO BACKGROUND OF THE INVENTION The extent and control of the combustion which takes place in an internal combustion engine has been the subject of extensive research for more than half a century with a principal objective of achieving high engine efficiency at the lowest possible fuel cost. In recent years ecologists, concerned with air pollution by carbon monoxide and unburned hydrocarbons, have given an added impetus to such research.

Attempts have been made to control the air-fuel ratio in a combustion process by sensors which measure one or more of a number of parameters; temperature, pressure, density of smoke, and the like. By way of example, Pierce, in U.S. Pat. No. 2,562,507, describes the I passing of a light beam through the exhaust gases in a flue in order to sense the density of smoke; a high density of smoke effecting the opening of a valve which increases the proportion of air in a combustion chamber. I

Bollo, in US Pat. No. 2,773,349, describes the sampling of an exhaust gas, the oxidation of the sample,

- and the analysis of the resulting oxidized exhaust gases SUMMARY OF THE INVENTION The present invention takes advantage of the fact i that liquid fuel in the typical carburetor flows from the float chamber to a venturi in the air line in response to a pressure differential. Control of fuel flow is achieved in the present invention by modifying the latter pressure differential responsively to changes in the thermal conductivity of, and hence the chemical analysis of, exhaust combustion gases in the exhaust pipe of the engine. Therefore, in an internal combustion engine provided with an exhaust pipe for exhaust gases and provided with a carburetor comprising a venturi and afloat chamber, the inventive improvement comprises: (a) a pressure modifying tube joining said venturi and said float chamber, (b) a valve in said tube, said valve being provided with a solenoid for controlling the movement of said valve, and (c) a thermal conductivity sensor positioned in said exhaust pipe and-electrically cooperative with said solenoid; wherein the position of said valve and the ratio of air to fuel provided to said engine by said carburetor is responsive to the thermal conductivity of said exhaust gases.

DESCRIPTION OF THE DRAWING The accompanying drawing illustrates, schemati- A carburetor, indicated generally at 20, comprises a float chamber 22, an inlet 24 for fuel, and a fuel outlet 26 leading to a fuel jet 28 positioned in a manner to deliver fuel to the venturi 16. The float chamber 22, further, is provided with a float 30 which cooperates with a valve 32 in the fuel inlet pipe 24 to maintain fuel at a predetermined level. A bleed orifice 34 is provided for relatively slow adjustment of the pressure in the float chamber 22 to ambient pressure outside the carburetor. A pressure modifying tube 36 joins the venturi 16 with a pressure modifying opening 38 in the float chamber 22. The latter opening 38 is provided with a valve 40 which is mounted for reciprocal motion in a solenoid 43 responsively to changes'in the current in the solenoid.

A sensor; in addition to the usual power source, amplifier, and standard electrical components (not shown); comprises a thermal conductivity cell 46 positioned in the exhaust pipe 14 and comprises an electrical circuit 48 which includes the windings of the solenoid 42.

DESCRIPTION OF OPERATION Liquid fuel enters the float chamber 22 of the carburetor 20 via the fuel opening 24. A float 30 in coopera tion with valve 32 via a pivot point 31 controls the level of the fuel. Air is drawn into the manifold 12 via the venturi l6 and past the throttle valve 18 because of the relatively low pressure in the manifold. Liquid fuel is sprayed into the air stream because of the relatively lower pressure in the venturi 16 as compared to the pressure in the float chamber 22. Combustion of the fuel occurs in the engine 10 and exhaust gases pass through the exhaust pipe 14.

The sensor 44 is initially calibrated against the thermal conductivity of mixtures of gases normally found in engine exhaust. In-this connection it is necessary to measure the thermal conductivity of mixtures from, on the one hand, an exhaust mixture resulting from combustion under very lean conditions to, on the other 'hand, an exhaust mixture resulting from combustion under very rich conditions. A thermal conductivity sensor such as described in the above mentioned US. Pat. No. 2,255,551 or any one of a number available commercially can be used.

The sensor circuit 48 is constructed such that a relatively large current flowing therein reflects the presence of a relatively high proportion of carbon monoxide and unburned hydrocarbons in the exhaust pipe or, in other words, reflects the need for relatively more air in the air-fuel mixture. The current in circuit 48 causes the solenoid to open the valve 40 in the pressure modifying opening 38. Opening the valve 40 permits modification of; that is, tends to decrease; the pressure differential between the venturi l6 and the float chamber 22. As the pressure in the float chamber 22 approaches the pressure in the venturi 16, relatively less fuel is sprayed into the air stream entering the manifold 12. The resulting, air-fuel mixture contains relatively more air and there is a reduction, in the exhaust pipe 14, of carbon monoxide and unburned hydrocarbons.

Similarily, and if the valve 40 is wide open, the resulting excessively lean conditions will lead to a small, or zero, current in the circuit 48 and the closing of the valve 40.

The position of the valve 40 (vertically, as shown) can be predetermined such that the valve 40 will be slightly opened to a point of maximum sensitivity to a. a pressure modifying tube joining said venturi with small changes in thermal conductivity of the exhaust said float chamber, gases at a predetermined optimum analysis of the exb. a valve in said pressure modifying tube and prohaust gases. In this manner the air-fuel ratio is made revided with a solenoid for controlling the opening sponsive to the analysis of the exhaust gases. 5 and closing thereof, and

It is apparent that changes and modifications can be c. a current generating, gas thermal conductivity senmade in the embodiment described without departing sor positioned in said exhaust pipe and electrically from the spirit or scope of the invention. cooperative with said solenoid;

I claim: wherein the position of said valve and consequently the 1. In an internal combustion engine provided with an ratio of air to fuel provided to said engine by said carexhaust pipe for exhaust gases and provided with a carburetor is responsive to the thermal conductivity of buretor comprising a venturi and a float chamber, the said exhaust gases. improvement which comprises: 

1. In an internal combustion engine provided with an exhaust pipe for exhaust gases and provided with a carburetor comprising a venturi and a float chamber, the improvement which comprises: a. a pressure modifying tube joining said venturi with said float chamber, b. a valve in said pressure modifying tube and provided with a solenoid for controlling the opening and closing thereof, and c. a current generating, gas thermal conductivity sensor positioned in said exhaust pipe and electrically cooperative with said solenoid; wherein the position of said valve and consequently the ratio of air to fuel provided to said engine by said carburetor is responsive to the thermal conductivity of said exhaust gases. 